\(C=1+1+\left(1-\frac{1}{4}\right)+\left(1-\frac{1}{9}\right)+\left(1-\frac{1}{16}\right)+...+\left(1-\frac{1}{2500}\right)\)

\(=\left(1+1+...+1\right)-\left(\frac{1}{4}+\frac{1}{9}+\frac{1}{16}+...+\frac{1}{2500}\right)\)

          51 số hạng                                    49 số hạng

= \(51-\left(\frac{1}{2.2}+\frac{1}{3.3}+\frac{1}{4.4}+...+\frac{1}{50.50}\right)\)

\(>51-\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{50.51}\right)=51-\left(\frac{1}{2}-\frac{1}{51}\right)=51-\frac{1}{2}+\frac{1}{51}\)

\(=50,5+\frac{1}{51}>50\left(đpcm\right)\)

Vậy C > 50

=33333.....3²

Ok chưa bạn,mình đưa về dạng lũy thừa.

my favourite food is meat

It's beef
 

Bài làm:

Ta có: \(3^{15}-9^6\)

\(=3^{15}-3^{12}\)

\(=3^{12}\left(3^3-1\right)\)

\(=3^{12}.26=3^{12}.2.13⋮13\)

=> đpcm

không biết nữa

Ta có : x² + 7x + 12 = 0

=> x² + 4x + 3x + 12 = 0

=> x(x + 4) + 3(x + 4) = 0

=> (x + 3)(x + 4) = 0

=> \(\orbr{\begin{cases}x+3=0\\x+4=0\end{cases}}\Rightarrow\hept{\begin{cases}x=-3\\x=-4\end{cases}}\)

Vậy \(x\in\left\{-3;-4\right\}\)

x² + 7x + 12 = 0

<=> x² + 3x + 4x + 12 = 0

<=> x( x + 3 ) + 4( x + 3 ) = 0

<=> ( x + 3 )( x + 4 ) = 0

<=> \(\orbr{\begin{cases}x+3=0\\x+4=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=-3\\x=-4\end{cases}}\)

Vậy S = { -3 ; -4 }

Hello everyone, my name is Yen. I am twelve years old. I am from Ngoc Thanh Village, Kim Dong district, Hung Yen province. Today, I am very happy to tell you about my school. My school is Le Quy Don. It is in Luong Bang town, Kim Dong district, Hung Yen province. It is very beautiful and big. There are twelve classrooms and eight function rooms in my shool. My school has five hundred and twenty-five students and thirty-two teachers. Students in my school are very good. They come from around Kim Dong district. Our teachers teach very well. At school, I learn many subject such as : Math, Literature, English, Art, Music,...In Math lessons, I learn how to count. In English classes, I learn how to speak English. In Music lessons, I sing songs. In Art classes, I draw pictures. So on...In all subject, I English best because it's very interesting and important for me. At breaks, I have a lots activities : skipping rope, hiding and seeking, chatting with friends, so on...Each day at school is a happy day. I love my school very much.

Hello everyone. My name is... I am ... years old .I live at ...street,.....district,.......province.Today,I am very glad to introduce my own day to you. My day starts at 5.30 am. When I get up , I'm used to (quen vs vc) doing exercises,brushing teeth,washing my face,... Then, I prepare my breakfast. I usually eat noodles or rice with meat and drink a cup of hot milk. After that, I get on my uniform and walk to school at 6.am. At school ,I study hard for the final grade in the secondary school. If the teacher asks a difficult question, I will ask my friends who can answer it to solve the question together. My class finishes at 11.30am. After finsh the class, I come back home and have lunch and take a rest to 1.30pm. My afternoon class starts at 2pm and finishes at 4.30 pm. When I come home ,I help my parents do the housework. Next, I do my homework before I take a bath. My family often has dinner at 7pm. After the dinner, I watch TV for half an hour and learn by heart the homework . At 12pm, I go to the bed . That is the end my own day.

P/S: mấy chỗ ....... bạn thêm thông tin của mk vào. Còn những chỗ gạch chân bạn có thể thay nó bằng những h/đ của mk.